Contributions to Zoology, 86 (4) – 2017Menno Schilthuizen; Rob Langelaan; Nicola Hemmings; Wesley van Oostenbrugge; Stefan Visser: An unexpected twist: Sperm cells coil to the right in land snails and to the left in song birds

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For the Stylommatophora, we obtained photographs of 514 sperm cells, from 27 individuals, belonging to 8 species, and 4 families (SI1). Although sperm morphology varied considerably (Figs. 1, 2), all cells, without exception coiled dextrally (SI2). For the Passeriformes, we obtained photographs of 486 sperm cells, from 26 individuals, belonging to 18 species, and 8 families (SI3). Here, overall morphology was more uniform (Fig. 3), all sperm cells coiled sinistrally (SI4).


Figure 1. Drawings of sperm cell heads of nine species of Pulmonata: a, Arianta arbustorum; b, Arion rufus; c, Arion subfuscus; d, Cepaea nemoralis; e, Cornu aspersum; f, Helix pomatia; g, Limax maximus; h, Succinea putris; i, Amphidromus inversus (a-h originals, drawn by Erik-Jan Bosch; i after Schilthuizen and van Heuven, 2011).


Figure 2. Scanning electron-micrographs of a sperm cell head among other sperm cells within a spermatophore for Cepaea nemoralis (top) and Arion subfuscus (bottom). Scale bar = 1 µm.


Figure 3. Scanning electron-micrographs of isolated sperm cell heads of various Passeriformes: a, Hippolais polyglotta; b, Hippolais icitrina; c, Acrocephalus scirpaceus; d, Phylloscopus sibilatrix; e, Phylloscopus collybita; f, Phylloscopus trochilus; g, Sylvia melanocephala; h, Sylvia atricapilla; i, Sylvia curruca; j, Cistothorus palustris; k, Prunella modularis; l, Emberiza citrinella; m, Turdus merula; n, Fringilla coelebs; o, Acanthis cabaret; p, Chloris chloris; q, Carpodacus erythrinus; r, Haemorhous purpureus. All sperm cell heads have been shown with the tail down, and the acrosome up. Scale bars always represent 1 µm.